1. Field of the Invention
The present invention relates to a nanowire light emitting device, and more particularly a new type of light emitting device employing a semiconductor nanowire and a manufacturing method thereof.
2. Description of the Related Art
In general, a semiconductor light emitting device is configured as a PN junction structure using a compound semiconductor epitaxial layer as shown in FIG. 1. That is, a nitride semiconductor light emitting device 10 includes a first conductivity type nitride layer 14, an active layer of a multi quantum well structure 15, and a second conductivity type nitride semiconductor layer stacked in their order on a substrate 11. Also, a first electrode 18 is connected to the first conductivity type nitride layer 14 and a second electrode 19 is connected to the second conductivity type nitride semiconductor layer 17.
Such a semiconductor epitaxial layer of the first conductivity type nitride layer 14, the active layer 15 and the second conductivity type nitride layer 17 suffers a crystal defect due to differences in lattice constant and thermal expansion coefficient, thereby significantly deteriorating light emitting properties of the device. The crystal defect is more severely manifested in a nitride semiconductor. Especially when required to contain a relatively great proportion of In, an InGaN layer of the active layer 15 tends to have its wavelength shortened due to phase separation during growth. This gravely undermines reliability of the device.
Furthermore, for the conventional semiconductor light emitting device to emit light of different wavelengths, the active layer needs to have different compositions. This renders it difficult to manufacture a monolithic white light emitting device.
Recently, a junction device using a nanowire or a nanostick, in place of the epitaxial layer just described, has been vigorously studied. The nanostick is a device having a diameter of 100 nm, which carries physical properties different from those of a bulk structure. FIG. 2a illustrates a light emitting display 20 using such nanowires 25.
The display device 20 as shown in FIG. 2a has a transparent substrate 21 and a cover substrate 26 connected via insulating structures 29. The transparent substrate 21 has a lower electrode layer 23 made of e.g., ITO formed thereon and the cover substrate 26 has an upper electrode layer 27 formed on an underside thereof. The nanowires 25 are disposed between the insulating structures 29. The nanowires 25 feature a coaxial cable structure in which a p-type semiconductor material 25a and an n-type semiconductor material 25b are formed in a growth direction, as shown in FIG. 2b. The nanowires 25 emit light of a specific wavelength when a voltage is applied to the upper and lower electrode layers 27 and 23. The light emitted is convertible into a desired wavelength by a phosphor layer 28 formed underneath the transparent substrate 21.
However, the aforesaid method, which uses the nanowire emitting light of a specific wavelength, needs to employ a separate phosphor layer in order to produce white light. Also, the nanowires, when directly deposited as a PN junction device as in FIG. 2a, are hardly miniaturizable and individually arrangeable in a precise manner.
As described above, the nanowire light emitting device hardly produces a desired light, especially white light, thereby failing to develop into a light emitting device.